The invention relates to an actuating system for modifying the position of the moving parts of a chair, seat or bed.
Applications of the invention may be found in all domains using a chair, seat or bed in which the moving parts may be activated electrically, as a function of the user""s needs or comfort. In particular, the invention is applicable to seats designed for the transport of passengers such as aircraft seats, wheelchairs, dentists"" chairs, medical seats or beds, electric stretchers, etc.
In many domains, chairs and seats with inclinable backs or inclinable beds are used either for user comfort, such as aircraft seats, or for practical reasons such as dentists"" chairs or wheelchairs.
Typically, the backs of chairs or seats (or beds) are inclined by means of an actuator made using a system of wheels and worm screws driven by a motor. This type of actuator is described particularly in patent U.S. Pat. No. 4 759 587.
However, in the case of these worm screw actuators, it is relatively difficult to block the mechanism (subsequently called irreversibility); thus, to achieve good irreversibility, the efficiency of the system is necessarily reduced. Therefore, use of this type of system requires a compromise between irreversibility and the actuator efficiency.
Furthermore, the coefficients of friction that determine the efficiency and irreversibility of this type of actuator fluctuate as a function of several parameters concerning the materials making up the actuator; in particular, they fluctuate as a function of the temperature and nature of lubrication of these materials.
Thus, when a worm screw actuator is used for a seat with a high static load, in other words a load greater than or equal to the dynamic capacity of the actuator itself, it is difficult to ensure good irreversibility; however a reduction in the efficiency must be accepted in order to obtain satisfactory irreversibility; therefore this actuator has a bad efficiency.
Furthermore, note also that as the efficiency drops, the value of the current necessary when the actuator is unloaded is high and variable due to friction; therefore sensitivity at a precise load is very low. Consequently, for seat movements for which the generated torque must be controlled, in other words in which the maximum force must be limited for safety reasons, it is very difficult if not impossible to adjust the safety threshold that must not be exceeded, given that this threshold must be sufficiently high so that the chair can be operated at nominal load, regardless of the situation.
Furthermore, poor efficiency of the actuator requires a large energy source, which causes an increase in the weight, volume and temperature rise of the system, and consequently high cost.
The purpose of the invention is precisely to overcome the disadvantages of the actuators mentioned above. Consequently, it proposes an electric actuator for which irreversibility (blocking of the mechanism) is independent of the efficiency and is obtained by a current release locking device installed in parallel on a motor and powered by the same control device as the motor.
More precisely, the invention relates to a system for modifying the position of the moving parts of a bed, chair or seat comprising:
mechanical means for the displacement of a first part free to move with respect to a second fixed or moving part of the bed, chair or seat,
actuation means fixed on the chair, seat or bed to activate or lock the said displacement means of the first part, characterized in that the actuation and locking means comprise:
an electric motor powered by a control device,
a rod driven by the motor,
a current release blocking device, that prevents movement of the rod, mounted in parallel with the electric motor and connected to the control device,
a transmission system driving the first part displacement means at a determined speed.
Advantageously, the current release blocking device is a brake which blocks the rod when there is no electricity power supply to it and which authorizes movement of the rod when it is powered.
According to this invention, the transmission system is a reduction gear with straight gear wheels.
According to one embodiment of the invention, the motor is a rotary motor driving the rod in a rotational movement.